Bulk crystalline 4h-silicon through a metastable allotropic transition

Abstract

A novel bulk form of 4H-Si, a crystalline allotrope of silicon and a novel method of manufacture. The novel material consists of highly oriented microcrystals of silicon in the 4H structure with no disordered material. The 4H-Si is derived from heating a second novel material Si24 under proper conditions. The allotrope of silicon is produced as bulk, microcrystalline agglomerates.

1 . A 4H—Si crystalline allotrope of silicon comprising the 4H structure with highly oriented microcrystals. 
     
     
         2 . The 4H—Si material of  claim 1 , wherein the microcrystalline 4H silicon phase has no disordered material. 
     
     
         3 . The material of  claim 1 , wherein:
 the 4H—Si exhibits unambiguous Raman spectra and X-ray diffraction patterns.   
     
     
         4 . The material of  claim 1 , wherein:
 the material exhibits the characteristics of an indirect band gap semiconductor with a band gap near 1.2 eV.   
     
     
         5 . The material of  claim 1 , wherein:
 4H—Si is produced by heating Si 24  between vacuum pressure (10 −3  torr) and 9 GPa at temperatures between 300-800° C. and structural conversion to 4H—Si is dependent on temperature and heating duration.   
     
     
         6 . The material of  claim 1 , wherein:
 structural conversion to 4H—Si occurs in the presence of iodine and when heating Na 4 Si 24  at temperatures between 300-800° C.   
     
     
         7 . The material of  claim 1 , wherein:
 the 4H—Si is in the form of highly oriented 4H—Si grains.   
     
     
         8 . The material of  claim 1 , wherein:
 the 4H—Si material is in the form of powdered 4H—Si.   
     
     
         9 . The material of  claim 8 , wherein:
 the 4H—Si powder has a grain sizes between approximately 0.4 microns and 0.6 microns.   
     
     
         10 . The material of  claim 1 , wherein:
 the 4H—Si phase has a lower-energy direct interband transition than the diamond-Si phase and exhibits significant differences in the conduction band minima, exhibits desirable elastic properties and wherein heterostructures are possible.   
     
     
         11 . A method of manufacture of 4H—Si from a starting material of Si 24  heated under proper conditions to produce an allotrope of silicon as bulk, microcrystalline agglomerates. 
     
     
         12 . The method of  claim 11 , wherein: the Si 24  starting material is heated above 300° C. at atmospheric pressure. 
     
     
         13 . The method of  claim 11 , wherein: the Si 24  starting material is heated to approximately 800° C. at a pressure near 9 GPa. 
     
     
         14 . The method of  claim 11 , wherein: the Si 24  starting material is heated through a metastable phase transformation. 
     
     
         15 . The method of  claim 11 , wherein:
 the 4H—Si is produced by heating Si 24  between vacuum pressure (10 −3  torr) and 9 GPa at temperatures between 300-800° C.   
     
     
         16 . A method of manufacture of 4H—Si from a starting material of Na 4 Si 24 , comprising:
 heating Na 4 Si 24  in the presence of iodine. 
 
     
     
         17 . The method of  claim 16 , wherein:
 structural conversion to 4H—Si from Na 4 Si 24  is dependent on temperature and heating duration.   
     
     
         18 . The method of  claim 11 , wherein:
 single-crystalline Si 24  results in highly oriented 4H—Si grains, whereas powder Si 24  results in powdered 4H—Si.   
     
     
         19 . The method of  claim 11 , wherein:
 samples are black powder or multicrystalline agglomerates with grain sizes near 0.5 microns.   
     
     
         20 . A 4H—Si crystalline allotrope of silicon comprising a highly oriented 4H phase silicon microcrystals structure with minimal disordered material. 
     
     
         21 . A 4H—Si crystalline allotrope of silicon comprising a highly oriented 4H phase silicon microcrystals structure synthesized from Si 24 . 
     
     
         22 . A 4H—Si crystalline allotrope of silicon comprising a highly oriented 4H phase silicon microcrystals structure synthesized from Na 4 Si 24 . 
     
     
         23 . A 4H—Si crystalline allotrope of silicon comprising a highly oriented 4H phase silicon microcrystals structure synthesized from Si 24  having properties enabling direct use as a semiconductor. 
     
     
         24 . A 4H—Si crystalline allotrope of silicon comprising a highly oriented 4H phase silicon microcrystals structure synthesized from Si 24  having 1.2 eV band gap properties enabling direct use as a semiconductor. 
     
     
         25 . The method of  claim 11 , comprising the further step of:
 applying strain via atomic Ge substitution to enhance the optical absorption properties.   
     
     
         26 . The method of  claim 11 , comprising the further step of:
 applying strain via atomic Ge substitution to increase charge mobilities.   
     
     
         27 . The method of  claim 11 , further comprising the step of:
 deposition growth with a mismatched lattice substrate to enhance the optical absorption properties.   
     
     
         28 . The method of  claim 11 , further comprising the step of:
 deposition growth with a mismatched lattice substrate to increase charge mobilities.   
     
     
         29 . The method of  claim 11 , comprising the further step of:
 using the synthesized 4H—Si as seed crystals for growing large volumes of 4H—Si with absorption and optoelectronic properties exceeding those of DC-Si.   
     
     
         30 . The method of  claim 11 , comprising the further step of:
 using the synthesized 4H—Si as seed crystals for growing large volumes of 4H—Si solar devices with absorption and optoelectronic properties complementing or exceeding those of DC-Si.